Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

Stabilization (i.e., the establishment of a vegetative cover) of these environments is essential to
the control of metal exposure or migration from soil/dust and groundwater pathways.
At Bunker Hill, ID, Brown et al. (2003b) demonstrated that a mixture of high nitrogen
biosolids and wood pulp or ash, when surface applied at a rate of approximately 50 and
220 tons/ha, respectively, increased soil pH from 6.8 to approximately 8.0, increased plant
biomass from 0.01 mg/ha to more than 3.4 tons/ha, and resulted in a healthy plant cover within
2 years. Metal mobility was more difficult to evaluate. Plant concentrations of Zn and Cd were
generally normal for the first 2 years of the study; however, Pb concentrations in vegetation
dramatically increased two to three times in the first year. Additionally, macronutrients (Ca, K,
and Mg) decreased in plant tissue.
Urban soils, whether contaminated from smelting, paint, auto emissions, or industrial
activity, are often contaminated with Pb (Agency for Toxic Substances and Disease Registry
[ATSDR], 1988) and can be a significant pathway to elevated child blood Pb levels (Angle et al.,
1974). Typically, contaminated residential soils are replaced under Superfund rules. However,
urban soils are less likely to be remediated unless a particular facility is identified as the
contaminate source. Application of biosolids to such soils may be a cost-effective means for
individuals or communities to lower Pb RBAs.
A field study by Farfel et al. (2005) using the commercial biosolid ORGO found that,
over a 1-year period, Pb in the dripline soils of one residence had reduced RBAs by ~60%.
However, soils throughout the remainder of the yard showed either no reduction in RBA or a
slight increase. A more complex study was conducted by Brown et al. (2003a) on an urban
dripline soil in the lab. The study used an assortment of locally derived biosolids (raw, ashed,
high-Fe compost, and compost) with and without lime. All amendments were incubated with
approximately 10% biosolids for a little more than 30 days. In vitro and in vivo data both
indicated a 3 to 54% reduction in Pb RBA, with the high-Fe compost providing the greatest
reduction.
As with phosphate amendments, problems with biosolid application have also been
documented. Studies have shown that metal transport is significantly accelerated in soils
amended with biosolids (Al-Wabel et al., 2002; McBride et al., 1997, 1999; Lamy et al., 1993;
Richards et al., 1998, 2000). Some of these studies indicate that metal concentrations in soil
solutions up to 80 cm below the amended surface increased by 3- to 20-fold in concentration up
AX7-21